The pattern of resting breathing in patients with upper airway obstruction

The flow-time curve of resting breathing was recorded in 14 patients (aged 36 +/- 16 yrs) with mild to moderate symptoms of upper airway obstruction (UawO) and compared to that of 28 matched, healthy controls (HC) in order to characterize the breathing pattern of such patients. The inspiratory time over total time (TI/Ttot) was higher in the patients (0.42; SD 0.04) than in HC (0.37; SD 0.04) (p less than 0.001), and tidal volume (VT) over TI was lower in patients (0.37; SD 0.07 l.s-1) than in HC (0.43; SD 0.09 l.s-1) (p less than 0.01). Inspiratory and expiratory peak flows at rest were also lower in the patients (p less than 0.001). In these, the mean to peak flow ratio of inspiration (0.74; SD 0.07) was higher than in HC (0.66; SD 0.04) (p less than 0.0005). This indicates a more rectangular wave of inspiration in the patients. All of these changes may be due to the increased inspiratory load. However, since the patients were breathing at rest with VT and flows far below their values on the maximal flow volume loop, the changes can also be interpreted as adaptive rather than imposed by absolute mechanical limitations.

Nose/mouth distribution of respiratory airflow in 'mouth breathing' children

Oro-nasal distribution of respiratory airflow was determined in 120 'mouth breathing' children by a minimally invasive computer-assisted method that employed a modified CPAP nasal mask/pneumotach and a head-out body plethysmograph. Resulting measurements were reproducible but clinical assessments correlated poorly with these values. Airflow distribution was almost identical in inspiration and expiration. 100% nasal breathing was found over a wide range of nasal resistances, many subjects with lips apart. Overall, the nasal fraction was negatively correlated with resistance and it was increased by topical decongestant. Decreasing nasal resistance with increasing age was confirmed, but corresponding changes in airflow distribution were not demonstrated. Quantitative assessment is advocated in clinical management of 'mouth breathers'.

Ventilatory mechanics in healthy calves during helium-oxygen breathing

The mechanics of breathing was investigated in six healthy calves breathing either air or a mixture of 79% helium and 21% oxygen (He-O2). Intrapleural pressure (Ppl) was measured with an esophageal balloon catheter and transpulmonary pressure was obtained by subtracting the mouth pressure (Pm) from Ppl. Respiratory airflow (V) was measured using a Fleisch pneumotachograph N degrees 3 and tidal volume (Vt) was electronically derived by integrating V with respect to time. Respiratory airflow, Vt, Ppl and Pm were simultaneously recorded while the calves breathed first air (1 min), secondly He-O2 (1 min) and finally air again (1 min). The pulmonary function values were calculated on the tracings and the He-O2 values were compared to the corresponding "air" values. The ventilatory response to resistance unloading was characterized by a significant increase in minute volume exclusively due to an increase in respiratory frequency, while Vt remained unchanged. A decrease of 32% in the total pulmonary resistance (RL) and 16% in the work per litre of ventilation (Wrm/l) were observed when calves breathed He-O2. The effect of the He-O2 on RL and on Wrm/l suggests that, in the bovine species, airflow turbulances in the upper part of the respiratory tract play a significant role in the total airways resistance.

Importance of inspiratory flow rate in the cough response to citric acid inhalation in normal subjects

1. The cough response to inhalation of citric acid is produced mainly by irritation of the larynx and trachea. Variations in the inspiratory flow rate might lead to changes in deposition of the drug, and consequently in the cough threshold. 2. We have studied the effect of three different inspiratory flow rates in 11 normal, non-smoking subjects (nine males, aged 23-39 years), who inhaled nebulized citric acid (2.5-640 mg/l). The test finished when a cough was produced at each inhalation (cough threshold) or the maximum concentration was reached. 3. The inspiratory flow rate was limited with a fixed resistance and displayed on a screen so that the subjects could reach a constant inspiratory flow rate of 50, 100 and 150 l/min with a submaximal inspiratory effort. 4. The mean (SD) inspiratory flow rates achieved were 51.4 (5.3), 86.2 (16.6) and 134.4 (22.9) l/min. Baseline forced expiratory volume in 1 s and functional vital capacity were not different on the 3 study days. 5. The cough threshold (geometric mean and 95% confidence intervals) was 21 (9-54) mg/l at an inspiratory flow rate of 50 l/min and 43 (13-141) mg/l at 150 l/min (P less than 0.05). The amount of drug tolerated by the subjects before the cough threshold was achieved was 5.2 (2.0-13.8) mg at an inspiratory flow rate of 50 l/min and 11.6 (3.4-39.8) mg at 150 l/min (P less than 0.05). The number of coughs per inhalation was 1.6 (1.1-2.0) at an inspiratory flow rate of 50 l/min and 1.1 (0.7-1.5) at 150 l/min (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Ventilatory effects of nasal continuous positive airway pressure

Nasal continuous positive airway pressure (nCPAP) improved arterial oxygenation in patients with sleep apnoea as well as those with acute pulmonary processes such as Pneumocystis carinii pneumonia. Despite an expanding pool of clinical information, little if any attempt seems to have been made to see whether nCPAP alters ventilatory patterns. The effect of nCPAP was assessed by respiratory inductance plethysmography in 14 healthy males. nCPAP reduced respiratory rate (14.3 +/- 1.47 to 9.7 +/- 1.98, p less than 0.0001) but increased tidal volume (0.483 +/- 0.090 to 0.602 +/- 0.140 l, p = 0.01). Accordingly, minute ventilation decreased (6.91 +/- 1.20 to 5.64 +/- 0.93 l.min-1, p = 0.0002). Duty cycle (TI/TTOT) decreased from 0.43 +/- 0.04 to 0.35 +/- 0.05 s during nCPAP (p less than 0.0001). Mean inspiratory time and mean expiratory time increased with nCPAP (1.79 +/- 0.19 to 2.20 +/- 0.41 and 2.44 +/- 0.38 to 4.27 +/- 1.07 s, respectively, p less than 0.02), but there were no significant changes in mean inspiratory flow rate or partitioning of rib cage and abdominal/diaphragmatic contributions to tidal volume. We conclude that nCPAP effects ventilatory pattern in a manner similar to that described for expiratory threshold loading; that is, by decreasing respiratory frequency and minute ventilation. nCPAP does not appear to stimulate healthy subjects to increase their level of ventilation.

[Initial expiratory activity as one of the criteria of the respiratory center function]

In 13 healthy men at rest and dosed muscular loads the authors studied maximal rates of the mouth pressure at the onset of inhalation and expiration (dP/dtI, dP/dtE) as well as the respiratory pattern. The parameter dP/dtE positively correlated with that of dP/dtI which reflects, as is known, an inspiratory activity of the respiratory center. The authors think that dP/dtE parameter can be used for noninvasive determination of expiratory activity.

Interaction between tracheal sound and flow rate: a comparison of some different flow evaluations from lung sounds

We simultaneously recorded tracheal sound and air flow from nine normal subjects (seven males and two females). Sound was picked up at the supra sternal notch with an air-coupled sensitive microphone held in a small airtight probe. Flow was measured at the mouth using a pneumotachograph Fleisch n degrees 2. Both sound and flow were directly digitized at a sampling rate of 5120 Hz and then divided in 128-sample blocks. For each sound block the frequency spectrum was computed using the fast Fourier transform. In order to evaluate instantaneous flow-rate from tracheal sounds we investigated eight methods divided in two groups of four. In the first group (i.e., reference curves methods), we assumed that a relationship existed between sound and flow and was thus reflected by the variations of certain parameters. We chose to use simple straightforward relationships, already known and published. We tested four different parameters. During a calibration phase, we built for each parameter P a reference curve representing the variations of P versus flow and being specific to each subject. Then, an unknown flow was evaluated in calculating P on a 128-sample block, and the reference curve gave the corresponding flow. In the second group, we made a hierarchial clustering analysis of sound spectra for revealing the frequency modifications, induced by the flow. We tested two kinds of spectra as well as two ways of associating a flow to a given cluster. This led us to four other methods for calculating the flow. All the eight methods but one gave a mean uncertainty in the measure of flow of about 15%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of lateral manual compression upon glottic incompetence: objective evaluations

Forceful manual compression of the thyroid and cricoid cartilages modifies the position, shape, and tension of the vocal folds. This is the basis of the four laryngeal manual compression tests, adjunctive examinations used as a means of preoperative assessment of patients for medialization laryngoplasty, ie, Isshiki thyroplasty types I and IV and arytenoid adduction. The laryngeal manual compression tests are simple to perform and noninvasive. Each of the four examinations yields valuable information on the effects on the voice of changes in vocal cord characteristics produced by manual compression. In this report, one of the four tests, lateral manual compression, is evaluated objectively with well-attested methods of videostroboscopic, aerodynamic, and acoustic analysis. The technique of performing lateral manual compression is described, and advantages and disadvantages are noted and compared in 10 patients. Preliminary findings in 4 patients in this group indicate that medialization laryngoplasty should be considered when test results are conclusive of effective glottic closure. Data derived in this preliminary study will be augmented as patients are added to the series.

Comparison of anaesthesia ventilators using a lung model

The ventilatory performance of six anaesthesia ventilators (Alphavent Drägerwerk; MCM 801 Ventilator Dameca; Ohmeda 7000 Ventilator and Ohmeda 7800 Ventilator Ohmeda; Servo Ventilator 900 D and Ventilator 710 Siemens-Elema) was tested in a lung model and compared with the ventilatory performance of the old Engström 300 (Gambro Engström). The lung model consisted of one tracheal tube, two bronchial tubes which could be partially occluded, and two lungs (glass jars filled with water to a suitable compliance). Dialled (set) minute volume was compared to recorded minute volume. Gas distribution between obstructed and non-obstructed lung was calculated. All ventilators had a linear relationship between dialled and measured volume. Only the Servo Ventilator 900 D produced a gas distribution which was as good as, or better than that produced by the Engström 300.

Pulmonary function and drug regimens in asthmatics

Overall function, persistent obstruction and control of potentially reversible wheeze were related to drug regimen in 624 patients attending review clinics. Pulmonary function before and after correction for the effects of age, duration of asthma and social factors was studied for each drug regimen. The performance of those on regular bronchidilators only, particularly non-smokers, was disappointing, particularly with regard to control of potentially reversible wheeze. There was a group of patients who expressed dissatisfaction with their condition in whom no change in management was made despite objective evidence of poor control of potentially reversible wheeze. Subjective assessment of control bore little relationship to actual function in those patients on oral steroids. Nevertheless, throughout the clinics as a whole, subjects recorded pulmonary function which was on average 80 per cent of their potential.

The pressure-flow method: some fundamental concepts

The pressure-flow method introduced by Warren and DuBois is a useful method for estimating velopharyngeal orifice area. However, this investigation shows that unless geometric similarity of subject and model exists, the value of the flow coefficient k used in the equation to estimate velopharyngeal orifice area cannot be established from model tests. Use of k = 0.65 is questioned as that value is typical of thin plate orifices, a geometry that is not a good representation of the velopharyngeal passage. Values of k from the literature and from steady state tests using a model similar to Warren's are presented to show the effect of various inlet shapes. The influence of inlet shape supports the conclusion that k may be significantly higher than 0.65, conceivably approaching values in the range of 0.9 to 0.97, depending on the orifice geometry.

Accuracy and reproducibility of the Assess peak flow meter

The variability of peak flow measurements was studied in 24 patients with airway obstruction, using 12 Assess peak flow meters and a Fleisch pneumotachograph type 4 as a standard. The Assess peak flow meter gave systematic under-readings of 19-34% (low accuracy). The value scale of the Assess peak flow meter should be adjusted. As systematic under-readings do not influence the variability in peak flow measurements, variability was only caused by the random error of the instrument. The random error of the Assess peak flow meter was relatively low: about 4% of the measured peak flow value (high precision). The contribution of the Assess peak flow meter to the total variability of peak flow measurements showed a linear relationship (r = 0.53) with the value of the peak flow rate itself and varied from 9% (at 3 l.s-1) to 86% (at 10.8 l.s-1). Reading errors of the peak flow meter were responsible for about 1% of the total variability. The remaining variability is probably caused by the correctness of the peak flow performance and the motivation of the patient.

Variation in maximum inspiratory and expiratory pressure after application of inspiratory loads in patients with COPD

We studied eight men with chronic obstructive pulmonary disease (COPD) (age, 60.57 +/- 7.59 years; height, 162 +/- 10.43 cm; weight, 65 +/- 9.7 kg). Functional values of the sample were as follows: FEV1, 46 percent; FVC, 67 percent; PO2, 72.4 mm Hg; and pH, 7.41. We used a modification of the Nickerson and Keens method. Patients were required to perform 65 percent of maximal inspiratory pressure (MIP). We counted the time from the start of the test to exhaustion of the patient (TLIM). We measured basal MIP and maximal expiratory pressure (MEP) (TLC) at the TLIM and 10, 20, and 30 minutes and MIP was different from the basal value (MIP basal, 85.7 cm H2O; MIP 10 minutes, 79.1 cm H2O; MIP 20 minutes, 78.6 cm H2O; MIP 30 minutes, 79.6 cm H2O. The MEP was not different from the basal value. We concluded that in patients with COPD, MIP decreases significantly after inspiration through umbral inspiratory weight equal to 65 percent MIP and does not return to basal value for 30 minutes. The MEP does not change with respect to basal determination.

Persistent hypoxemia and excessive daytime sleepiness in chronic obstructive pulmonary disease (COPD)

Fourteen patients with chronic obstructive pulmonary disease (COPD) and chronic hypoxemia were studied to evaluate the relationship between hypoxemia and objective and subjective daytime sleepiness. Patients were selected with a waking PaO2 of less than 70 mm Hg and less than 50 percent predicted FEV1. Clinically, none of these patients had complaints of significant daytime sleepiness. Each patient underwent standard all-night polysomnographic evaluation followed by a multiple sleep latency test (MSLT). There was no significant correlation between the mean sleep onset latency for the MSLT and the waking PaO2, PCO2, FEV1, or spontaneous desaturations during sleep. Patients with COPD exhibited a mean MSLT that was within normal limits, despite a short total sleep time and numerous arousals from sleep. We conclude that there appears to be no relationship between chronic daytime hypoxemia and subjective reports and objective measures of daytime sleepiness.

Experimental determination of a unit of song production in the zebra finch (Taeniopygia guttata)

Zebra finch (Taeniopygia guttata) song is composed of syllables delivered in a set order. Little is known about the program that controls this temporal delivery. A decision to sing or not to sing may or may not affect the entire song. Song, once commenced, may continue or may halt. If song is halted, stops may occur only at certain points. Seven zebra finches were presented with short bursts of strobe light while engaged in song. The variables of interest were whether the birds stopped and where they stopped. The results can be summarized as follows: Ongoing zebra finch song can be interrupted, interruptions occur at discrete locations in song, and the locations almost always fall between song syllables. These results reveal a functional representation of song production and place constraints on possible neural mechanisms that underlie song production in zebra finches and probably other oscine species. The results also raise hypotheses about the elements of song perception and memory.

The effect of air flow and medial adductory compression on vocal efficiency and glottal vibration

This study used an in vivo canine model to investigate the effects of varying vocal fold resistance by electrically stimulating the recurrent laryngeal nerve while monitoring medial adductory compression of the vocal folds, glottal airflow, and vocal intensity. The effects of increasing airflow on glottal vibration were also examined stroboscopically and by measurement of open quotient. The results indicated that increasing intensity by medial adductory compression was more efficient than by increasing airflow. Increasing airflow produced a significantly greater open quotient and vocal fold vibratory excursion.

Comparison of flow-resistive work load due to humidifying devices

There are many kinds of humidifying devices. We evaluated six humidifiers from the viewpoint of AWLs. The AWL was obtained by calculating the area difference between pressure-volume tracings obtained without and with humidifiers. To examine the effect of pressure monitoring sites on AWL when a humidifier is placed, we measured AWL at three different pressure monitoring sites. The AWL was affected significantly by the pressure monitoring site for the ventilator. When a pressure monitor sensor was placed on the inspiratory limb between the inspiratory valve and humidifiers, the ventilator was not able to compensate for the pressure drop caused by impedance characteristics of the humidifier equipment. This resulted in significant inspiratory AWL on the patient. Thus, humidifying devices should be carefully selected from the viewpoint of not only humidifying capability but also AWL. Furthermore, we must recognize the importance of the pressure monitoring site for the ventilator.

Upper airway measurements predict response to uvulopalatopharyngoplasty in obstructive sleep apnea

Although uvulopalatopharyngoplasty relieves obstructive sleep apnea in the majority of patients, the factors that determine a successful response are not well defined. To determine whether preoperative awake upper airway measurements predict the response to uvulopalatopharyngoplasty, presurgical lateral cephalometric radiographs were evaluated on 60 consecutive patients with symptomatic obstructive sleep apnea. Patients underwent overnight polysomnograms before uvulopalatopharyngoplasty and 3 months afterwards. Forty-eight (80%) patients had a good response as defined by a postoperative apnea index of less than or equal to 4 apneas/hour or a reduction in apnea index of greater than or equal to 60%. Responders had a significantly narrower inferior airway space (P less than .0005) and a smaller ratio of inferior airway space to tongue length (P less than .001). Improvement in apnea severity following uvulopalatopharyngoplasty was related to the degree of airway narrowing (r = 0.36; P less than .01). This study shows that upper airway measurements help predict response to uvulopalatopharyngoplasty in patients with obstructive sleep apnea. Patients with a narrow airway, particularly relative to tongue size, have good responses to uvulopalatopharyngoplasty.

Airway function in infants with vascular rings: preoperative and postoperative assessment

Aortic arch anomalies in infancy often cause intrathoracic airway obstruction. Airway function was assessed as part of the diagnostic evaluation in six symptomatic infants both by plethysmography and using a chest compression technique to obtain partial flow-volume loops. Two infants had normal intrathoracic airway function and their symptoms were unrelated to aortic arch abnormalities. The remaining four had complete vascular rings (three double aortic arch, one pulmonary sling) and had increased expiratory airway resistance (Raw) (mean Raw = 700% predicted) and greatly decreased maximum flow rates at functional residual capacity (VmaxFRC; mean VmaxFRC = 34% predicted) with gross shape abnormalities of the flow-volume loop. Postoperatively airway function was substantially improved (mean Raw = 175% predicted, VmaxFRC = 79% predicted) but some abnormality of flow-volume loop shape remained, suggesting that tracheal dynamics were not completely normal in the early postoperative period.

Effect of age on changes in flow rates and airway conductance after a deep breath

The effects of aging on changes in maximal expiratory flow rates and specific airway conductance after a deep breath were evaluated in 64 normal subjects. Flow rates (Vp) on partial expiratory flow-volume curves (PEFV), initiated from 60-70% of the vital capacity (VC), were compared with those (Vc) on maximal flow-volume curves (MEFV), initiated from total lung capacity (TLC), at a lung volume corresponding to 25% of VC on the MEFV curves. Specific airway conductance was measured before (sGaw) and after a deep inspiration (sGawDI). Bronchodilation after inspiration to TLC was inferred by Vp/Vc less than 1 and sGaw/sGawDI less than 1. The mean Vp was less than Vc. However, the ratio Vp/Vc increased significantly with age (r = 0.75, P less than 0.001). Specific conductance also increased after a deep inspiration (sGaw less than sGawDI). The ratio sGaw/sGawDIj increased slightly but significantly with age (r = 0.28, P less than 0.02). Measurement of lung elastic recoil pressures before and after a deep breath in a subgroup of patients (n = 14) suggested that the age-related increase in Vp/Vc was secondary to a decrement in the ability of a deep breath to decrease the upstream airway resistance. These findings suggest that even though changes in airway size after a deep breath as measured by sGaw/sGawDI have minimal age dependence, aging diminishes expiratory flow rates of MEFV curves relative to PEFV curves because of a decrease in the ability of a deep breath to increase the size of the peripheral airways.

Diameters, generations, and orders of branches in the bronchial tree

Studies of bronchial tree data by West et al. (J. Appl. Physiol. 60: 1089-1097, 1986) have shown that plots of mean diameter against generation, using log-log scales, can be represented by a power function with harmonic modulations. Other studies have shown that the mean diameter of the airways is exponentially related to order of branching. This paper demonstrates that both observations are compatible with a fractal model of branching, and because airway branching is fractal, this may explain why both are also true of the bronchial tree. Furthermore, the exponential relationship of mean diameter with generation in the larger airways, demonstrated by Weibel, is shown to result from the exponential relation of diameter with order in the fractal model.

Pulmonary function in obstructive sleep apnea. Relationships to pharyngeal resistance and cross-sectional area

Reduction in the size of the pharynx and increased pharyngeal airflow resistance have been demonstrated in patients with obstructive sleep apnea (OSA). We evaluated 15 men with severe OSA and 10 nonapneic control subjects matched for age and weight in order to determine if PCSA, inspiratory pharyngeal airflow resistance, and abnormal breathing events during sleep were associated with alterations in the flow-volume relationship and other awake PFTs. Pharyngeal cross-sectional area was determined by CT, and pharyngeal resistance between choanae and epiglottis was measured during quiet awake breathing. In patients with OSA, there was an inverse relationship between the mean cross-sectional area of the oropharynx and the ratio of FEF50%/FIF50% (rs = -0.54; p = 0.03). In all subjects, pharyngeal resistance was inversely related to percentage of predicted values for FEF25-75% (rs = -0.56; p = 0.01). The frequency of apneas during sleep was significantly (p less than 0.05) related to the percentage of predicted values for MVV, TLC, FVC, and PIF. Obesity appears to account for the strength of these relationships. Flow-volume loops and other PFTs did not distinguish patients with OSA from controls.

[Impedance of the respiratory tract of healthy newborn infants--studies using the polyfrequency oscillation method]

Resistance and reactance of the respiratory tract of 40 healthy newborn were measured by means of the polyfrequent oscillation method. Mean resistance had frequency-dependent values between 20.91 and 9.63 cm H2O per litre per second and mean reactance between -29.11 and -3.81 cm H2O/1/s. The resistance--but not the reactance--was found to depend on the body length and the body weight of the infants.

Responses to negative pressure surrounding the neck in anesthetized animals

Continuous positive pressure applied at the nose has been shown to cause a decrease in upper airway resistance. The present study was designed to determine whether a similar positive transmural pressure gradient, generated by applying a negative pressure at the body surface around the neck, altered upper airway patency. Studies were performed in nine spontaneously breathing anesthetized supine dogs. Airflow was measured with a pneumotachograph mounted on an airtight muzzle placed over the nose and mouth of each animal. Upper airway pressure was measured as the differential pressure between the extrathoracic trachea and the inside of the muzzle. Upper airway resistance was monitored as an index of airway patency. Negative pressure (-2 to -20 cmH2O) was applied around the neck by using a cuirass extending from the jaw to the thorax. In each animal, increasingly negative pressures were transmitted to the airway wall in a progressive, although not linear, fashion. Decreasing the pressure produced a progressive fall in upper airway resistance, without causing a significant change in respiratory drive or respiratory timing. At -5 cmH2O pressure, there occurred a significant fall in upper airway resistance, comparable with the response of a single, intravenous injection of sodium cyanide (0.5-3.0 mg), a respiratory stimulant that produces substantial increases in respiratory drive. We conclude that upper airway resistance is influenced by the transmural pressure across the airway wall and that such a gradient can be accomplished by making the extraluminal pressure more negative.(ABSTRACT TRUNCATED AT 250 WORDS)

Frequency, tidal volume, and mean airway pressure combinations that provide adequate gas exchange and low alveolar pressure during high frequency oscillatory ventilation in rabbits

We studied healthy and saline lavaged rabbits during high frequency oscillatory ventilation to determine what combination of frequency (f), tidal volume (Vt), and mean airway pressure (Paw) produced the lowest peak-to-peak alveolar pressure amplitude (Palv) and physiologic blood gas tensions. Sinusoidal volume changes were delivered through a tracheostomy by a piston pump driven by a linear motor. Tracheal pressure amplitude (Ptr) was measured through a tracheal catheter and alveolar pressure amplitude was measured in a capsule glued to the right lower lobe. PaO2, PaCO2, Ptr, and Palv were measured at the following settings: FiO2 = 0.5, frequency 2-28 Hz, Vt 1-3 mL/kg (50 150% dead space) and Paw 5-15 cm H2O. Many combinations of frequency and Vt resulted in the same PaO2 and PaCO2. Paw had a large effect on Palv and minimal effect on blood gas tensions. In lavaged rabbits, the composite variable f x Vt2 described the trends in Palv and blood gas tensions. As the product of f x Vt2 increased, PaO2 initially increased and then decreased, whereas PaCO2 decreased and Palv increased. No single combination of frequency, Vt and Paw simultaneously provided the lowest Palv and physiologic blood gas tensions. Adequate blood gas tensions and low Palv were obtained at frequencies less than 12 Hz, a Vt of 2 mL/kg and a Paw of 10 cm H2O. In healthy and lavaged rabbits PaO2 increased and PaCO2 decreased as frequency increased at lower Vt.PaO2 decreased as frequency increased at higher Vt in lavaged rabbits only. Palv tended to be greater in lavaged rabbits.

Titration of continuous positive airway pressure by the pattern of breathing: analysis of flow-volume-time relationships by a noninvasive computerized system

Infants can defend or even dynamically elevate their functional residual capacity with additional respiratory muscle work by retarding early expiratory airflow (V) with postinspiration inspiratory muscle activity and/or laryngeal narrowing, or by starting inspiration before expiration to the relaxation volume has been completed. In order to study the effect of continuous positive airway pressure (CPAP) on both phenomena in 23 infants (birthweight 1,746 +/- 417 g), we elevated the airway pressure stepwise in 0.2 kPa increments. A computerized bedside flow-volume (V/V) analysis was used for evaluation. In 16 "responders" early expiration braking decreased and "premature inspiratory interruption" was postponed at an "appropriate CPAP level." The linear segment (relaxation line) of the V/V-loop was lengthened until expiratory time reached a maximum. Elevation of CPAP beyond this level again produced a rapid, shallow pattern, often combined with flow acceleration late in expiration (recruitment of expiratory muscles). In the remaining seven infants (non-responders) these latter signs of excessive airway pressure already occurred at the lowest CPAP levels applied during the "titration trials." Respiratory rate without CPAP was different between responders (84 +/- 17/min) and non-responders (46 +/- 17/min). This approach for determining the appropriate CPAP level might reduce the risk of respiratory muscle fatigue.

Accurate measurement of blood alcohol concentration with isothermal rebreathing

The importance of interaction of exhaled air with the airway surface was evaluated by comparing the effects of different breathing maneuvers and inhaled air temperature on the relationship between breath alcohol concentration (BRAC) and blood alcohol concentration (BAC). Breath alcohol was measured with an infrared absorption unit. Blood and simulator liquid alcohol concentrations were measured by gas chromatography. Breath samples were measured after both low and high exhaled volumes and after rebreathing. Breathing maneuvers were performed after either hyperventilation, breathhold or normal breathing. Inspired air temperature was varied between 0 degree C and 40 degrees C. The rebreathing method for sampling alveolar alcohol samples was evaluated with a new isothermal rebreather that was designed to provide a substantial amount of heat to the rebreathed air in order to heat the airway surfaces. Using a single breath test, the indicated BAC values vary from 14% above the actual BAC to as low as 55% below the actual BAC. Hyperventilation caused a significant decrease in BRAC and breathhold caused a significant increase in BRAC. When isothermal rebreathing is applied to such tests, the breath test results were always within +/- 10% of the true BAC, even with an altered breathing pattern. Isothermal rebreathing provided an accurate sample of alveolar air that was not affected by altered breathing pattern or air temperature.

Nasometric and phototransductive measurements of reaction times among normal adult speakers

The temporal relationship among laryngeal, velopharyngeal, and labial activity was investigated by studying the reaction times of eight normal adults. Four female and four male subjects sustained production of the nasal consonant /m/ until a computer-driven imperative tone was presented at which time they were required to say /pi/ as quickly as possible. This task was repeated 30 times for each subject. The offset of voicing at the end of the /m/ and the onset of bilabial plosive release were monitored using a commercially available Nasometer. The onset of velopharyngeal (V-P) movement toward closure and the attainment of closure were monitored using a photodetector system. Across 240 responses, the average latencies were: 146 ms for initiation of V-P movement toward closure, 224 ms for voicing offset, 280 ms for onset of V-P closure and 317 ms for onset of plosive release. The significance of these findings is discussed with respect to speech motor control and the clinical evaluation of patients with velopharyngeal impairments.

Studies of wall shear and mass transfer in a large scale model of neonatal high-frequency jet ventilation

The problem of endotracheal erosion associated with neonatal high-frequency jet ventilation (HFJV) is investigated through measurement of air velocity profiles in a scaled up model of the system. Fluid mechanical scaling principles are applied in order to construct a model within which velocity profiles are measured by hot-wire anemometry. The effects of two different jet geometries are investigated. Velocity gradients measured near the tracheal wall are used to measure the shear stresses caused by the jet flow on the wall. The Chilton-Colburn analogy between the transport of momentum and mass is applied to investigate tracheal drying caused by the high shear flow. Shear forces are seen to be more than two times higher for jets located near the endotracheal tube wall than for those located axisymmetrically in the center of the tube. Since water vapor fluxes are dependent on these shears, they are also higher for the asymmetric case. Fluxes are shown to be greatly dependent on the temperature and relative humidity of the inspired gas. Water from the tracheal surface may be depleted within one second if inspired gases are inadequately heated and humidified. It is recommended that the design of neonatal HFJV devices include delivery of heated (near body temperature), humidified (as close to 100% humidity as possible) gases through an axisymmetric jet to best avoid the problem of endotracheal erosion.

Forced unilateral nostril breathing: a technique that affects brain hemisphericity and autonomic activity

Asymmetrical shoulder, thoracic and buttock pressure affect ipsilateral nasal resistance, autonomic tone, and hemisphericity. This factor must be taken into consideration when conducting psychological experimentation, and, in fact, may have confounded much prior research.

Respiratory changes with deep diving

Deep diving refers to saturation diving to a depth of more than 180 m (1.9 MPa ambient pressure). In the 1990s diving to 400 m may be necessary on the Norwegian continental shelf. The safety margins are narrow and the respiratory system is subject to great strain at such depths. The respiratory resistance increases and the dynamic lung volumes are reduced as the pressure increases due to enhanced gas density. Helium is used together with oxygen as breathing gas and its lower density partly normalises the dynamic lung volumes. The respiratory system puts clear limitations on intensity and duration of physical work in deep diving. Systematic studies of lung mechanics, gas exchange and respiratory regulation in the different phases of deep dives are lacking. Detection of occupational respiratory disorder following diving are dependent on long-term follow-up.

[Aerodynamics of respiratory flow in the nasopharynx]

The authors present a new technique for studying airflow patterns and particle deposition in the nasopharynx. The nasal cavities and the nasopharynx from the head of a human cadaver were filled with siliconrubber and a "positive" model was then produced by moulding with plastic. An apparatus was constructed to provide calibrated flow of propandiol in both directions. Flow characteristics were visualized by introducing small particles in suspension or by injecting methylene blue with a needle. In addition, test aerosol was drawn in through the model to demonstrate dust deposition sites in the nasopharynx. In the future, this method will enable us to examine the nasopharyngeal airflow patterns and deposition sites of inhaled particles.

Mechanisms of gas exchange with different gases during constant-flow ventilation

To investigate the mechanisms responsible for the difference in gas exchange during constant-flow ventilation (CFV) when using gases with different physical properties, we used mixtures of 70% N2-30% O2 (N2-O2) and 70% He-30% O2 (He-O2) as the insufflating gases in 12 dogs. All dogs but one had higher arterial PCO2 (PaCO2) with He-O2 compared with N2-O2. At a flow of 0.37 +/- 0.12 l/s, the mean PaCO2's with N2-O2 and He-O2 were 41.3 +/- 13.9 and 53.7 +/- 20.3 Torr, respectively (P less than 0.01); at a flow rate of 0.84 +/- 0.17 l/s, the mean PaCO2's were 29.1 +/- 11.3 and 35.3 +/- 13.6 Torr, respectively (P less than 0.01). The chest was then opened to alter the apposition between heart and the lungs, thereby reducing the extent of cardiogenic oscillations by 58.4 +/- 18.4%. This intervention did not significantly alter the difference in PaCO2 between N2-O2 and He-O2 from that observed in the intact animals, although the individual PaCO2 values for each gas mixture did increase. When the PaCO2 was plotted against stagnation pressure (rho V2), the difference in PaCO2 between N2-O2 and He-O2 was nearly abolished in both the closed- and open-chest animals. These findings suggest that the different PaCO2's obtained by insufflating gases with different physical properties at a fixed flow rate, catheter position, and lung volume result mainly from a difference in the properties of the jet.

Optimum stimulus frequency for contracting the inspiratory muscles with chest-surface electrodes to produce artificial respiration

Electroventilation is the term used to describe the production of inspiration by applying a train of short-duration pulses to chest-surface electrodes. Studies were conducted in the dog to determine the optimum frequency to produce a smooth air flow in the trachea. It was found that a stimulus frequency of 25/sec or slightly higher meets this criterion. To illustrate that electroventilation can be carried out for a prolonged period using these parameters, electroventilation was applied continuously for 5 hours in a dog without a noticeable change in blood pressure.

The relationship between nasal airway size and nasal-oral breathing in cleft lip and palate

Clefts of the lip and palate generally result in reduced size of the nasal airway. Procedures such as the placement of a pharyngeal flap tend to further compromise nasal breathing. The purpose of this study was to determine how size of the nasal airway affects the mode of breathing in adults with cleft lip and/or palate. A heterogeneous population of 50 adult subjects with cleft lip and/or palate was studied. Nineteen of the subjects had pharyngeal flaps. Respiratory inductive plethysmography was used in combination with an integrating pneumotachograph to measure percent nasal breathing. Pressure-flow studies were used to estimate nasal airway size. The data revealed that a majority of subjects had an airway size of less than 0.4 cm2, which constitutes impairment. Mean cross-sectional area for all subjects was 0.38 cm2 +/- 0.20 SD. Seventy percent of the subjects studied were oral breathers to some extent. A Spearman rank correlation coefficient of 0.725 (p less than 0.0001) indicated that oral-nasal breathing mode was related to airway size. Airway size in the subgroup with pharyngeal flaps was even smaller (0.31 cm2), while percent nasal breathing was lower. Mouthbreathing was observed in all subjects whose airway size was less than 0.38 cm2.

Peak flow nasal patency indices in patients operated for nasal obstruction

In 26 patients undergoing operation for nasal obstruction, nasal and oral peak expiratory and inspiratory flow rates were measured preoperatively and 1 month postoperatively. Peak expiratory and inspiratory flow nasal patency indices were calculated from the ratio between the nasal and oral peak flow rates. Postoperatively, these indices were significantly increased for the total nose and for the preoperatively worse nasal cavity. No significant change was observed for the oral peak flow rates. A significant preoperative difference in nasal patency between the two nasal cavities was eliminated by surgery, as the postoperative peak flow of each nasal cavity reached 80% of the peak flow of the total nose on expiration and close to 50% on inspiration. A good correspondence between the subjective improvement of nasal patency and the increase in peak expiratory and inspiratory flow nasal patency indices was observed for the total nose. These findings show that peak flow nasal patency indices give valuable information pre- and post-operatively in patients undergoing nasal surgery and that the method is simple and easy to perform.

Improved frequency response of pneumotachometers by digital compensation

To measure impedance one measures or estimates flow, which is commonly done by measuring the pressure drop across a pneumotachometer. The frequency response characteristics of standard pneumotachometer/pressure transducers (PPT) limit their use to relatively low frequencies. Also, the frequency response of PPTs has been reported to be "load" dependent. Thus, the frequency response characteristics measured under "no-load" conditions, which theoretically could be used to compensate subsequent measurements, may not be appropriate for measurements made under loaded conditions. Another method of measuring impedance exists which depends on a reference impedance element other than a pneumotachometer. In this method, an oscillatory flow signal with known amplitude is generated and used to force the system being tested. Unlike PPTs, this oscillatory flow generator (OFG) is a closed system that allows measurements to be made only during breath holding. Our objective was to determine whether the frequency response of a PPT could be compensated using measurements made under no-load conditions, such that it accurately measured an impedance load. The frequency response of the PPT under no-load conditions was measured by the OFG and used to compensate the output of the PPT in subsequent impedance measurements. The compensated PPT was used to measure the impedance of a mechanical structure and the impedances of four human subjects. The impedances of the mechanical structure and the subjects were also measured using the OFG.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of age on nasal cross-sectional area and respiratory mode in children

Although nasal cross-sectional size has been reported for adults, no information is available concerning the effects of age on nasal area and breathing mode in children. Determination of the effect of age on nasal size is necessary in order to define nasal airway impairment in children. The purpose of this study was to determine mean nasal cross-sectional size in children between the ages of 6 and 15 years. One hundred two children were assessed during resting breathing. The pressure-flow technique was used to estimate nasal cross-sectional size, and inductive plethysmography was used to assess nasal-oral breathing. The results indicate that nasal airway size increased approximately 0.032 cm2 each year. Mean nasal cross-sectional area increased from 0.21 +/- 0.05 cm2 at age 6 to 0.46 +/- 0.15 cm2 at age 14. The percentage of nasal breathing also increased with age.

Maintaining speech pressures in the presence of velopharyngeal impairment

Most, but not all, individuals with velopharyngeal inadequacy maintain consonant pressures greater than 3 cm H2O even with decreased velar resistance. The purpose of this study was to identify variables that might differentiate those who achieve adequate pressures from those who do not. Forty-four cleft lip and/or palate subjects were assessed during production of /p/ in the word "hamper." Twenty-three subjects achieved pressures greater than 3 cm H2O and 21 did not. The pressure-flow technique was used to assess velopharyngeal orifice size, nasal resistance, velar resistance, and nasal airflow during speech. Nasal cross-sectional area was measured during breathing. The data were analyzed by age and gender. Results indicate that the inability to achieve adequate consonant pressures in the presence of velopharyngeal inadequacy is more likely to occur in adults than in children. Although children are known to produce consonants at higher pressures than adults, the age disparity between groups did not account for the pressure differences. The most significant factor differentiating adequate and low pressure speakers was the magnitude of nasal plus velar resistance. This difference was consistent across age and gender.

A comparison of noninvasive procedures to assess nasal airway resistance

Through sophisticated equipment has been used to determine nasal airway resistance (Rnaw), data must be interpreted cautiously because of the variability of procedures used to obtain the measures. The present investigation was designed to determine the effects of breathing versus a speech task, using a forward versus a resting tongue carriage, and the consistency of these measures on Rnaw values. Twenty young adult females performed a noninvasive procedure for assessment of Rnaw during rest breathing and nasal/m/ sound production with and without tongue anchoring over a 2-day period. No significant differences in Rnaw were found between days or tasks. Of the tasks examined, sustained/m/production and tongue anchoring procedures proved consistent adjuncts to quiet breathing for estimation of nasal airway resistance across days and airflow rate conditions. Clinical implications for the application of these procedures are discussed.

Breathing patterns in asthmatic children during attack

Breathing patterns in asthmatic children during attack were studied using multielectrode impedance pneumography. A great number of respiration patterns were analyzed by a personal computer. During severe attacks, a pattern of prolonged expiratory time was noted. Inspiratory time, however, did not change, regardless of the severity of the asthmatic attack. No remarkable changes in breathing patterns were recognized during mild attacks. It was, therefore, considered that breathing patterns remained essentially unchanged except in cases of severe asthmatic attacks.

Evaluation of a turbine flow meter (Ventilometer Mark 2) in the measurement of ventilation

We have evaluated a turbine flow meter (Ventilometer Mark 2, PK Morgan, Kent, UK) at low flow rates and levels of ventilation which are likely to be encountered during exercise in patients with chronic respiratory disease. Pulsatile flows were generated from a volume-cycled mechanical ventilator, the flow wave-form was modified by damping to simulate a human breathing pattern. Comparative measurements of ventilation were made whilst varying tidal volume (VT) from 0.22 to 1.131 and respiratory rate (fR) from 10 to 35 min-1. At lower levels of ventilation the instrument tended to underread especially with increasing fR. The calibration factor must be adjusted to match the level of ventilation if the measurement errors are to be within 5%.

Pulmonary mechanics and energetics of normal, non-ventilated low birthweight infants

Pulmonary mechanics and energetics were determined in 33 healthy low birthweight infants (less than 1,500 g, 28-34 weeks gestation) who had never received ventilatory support. Tidal volume, dynamic pulmonary compliance, pulmonary resistance, pressure-volume relationships, and tidal flow-volume measurements were obtained by pneumotachography and the esophageal balloon technique. Standardized data collection and software data analysis by least mean squares technique yielded data at 0.5, 1, 2, and 4 weeks postnatally, as a function of gestational age (less than 30, 30-32, and greater than 32 weeks gestation). Relatively stable values were obtained for tidal volume and minute ventilation (normalized for body weight); these were associated with values of peak-to-peak esophageal pressure significantly (P less than 0.001) increasing from 4.4 +/- 0.3 SEM cmH2O at 0.5 weeks to 8.1 +/- 0.8 SEM cmH2O at 4 weeks of age. Dynamic pulmonary compliance ranged from 2.0 to 2.4 mL/cmH2O in the first 4 weeks of life. When normalized for weight, compliance decreased with age, which may suggest a slower pulmonary maturation as compared to increase of body weight. Mean pulmonary resistance decreased from 62.9 cmH2O/L/s at less than 30 weeks gestation to 32.5 cmH2O/L/s at greater than 32 weeks gestation, 0.5 weeks postnatally. Pulmonary resistance peaked at 2 weeks postnatally (P less than 0.05), at all gestational ages, then decreased. Changes in pulmonary mechanics resulted in increasing resistive work of breathing. Our findings suggest a postnatal retardation of pulmonary and airway growth, relative to gestation maturation. These data can provide an objective base of comparison for data in sick, low birthweight neonates.

What are the mechanisms producing increased ventilation in dead space studies in neonates?

In 21 studies on 15 infants an additional dead space tube produced a significant rise in end-tidal PCO2 and fall in end-tidal PO2, associated with a rise in minute ventilation (228 +/- 77 mL/kg/min at zero, 348 +/- 85 mL/kg/min at one, and 437 +/- 128 mL/kg/min at two anatomical dead spaces). The differences between end-inspiratory and end-expiratory PCO2 and PO2 did not change significantly, suggesting an increase in dead space, but not in alveolar ventilation. In a further 9 babies the rise in ventilation was unchanged when measurements were repeated in 30% oxygen (361 +/- 65 vs. 340 +/- 54 mL/kg/min at one anatomical dead space). Studies on 8 babies, with the added tube ventilated by a fan, showed that a mean 28% of the rise in minute ventilation was due to increased resistance. Although the response to tube breathing in neonates is complex, carbon dioxide appears to be the major factor producing increased ventilation.

Ultrasonic vocalizations by rat pups in the cold: An acoustic by-product of laryngeal braking?

Isolated rat pups respond to cold exposure physiologically by increasing metabolic heat production and behaviorally by emitting ultrasound. The relationship between these 2 responses was investigated by monitoring oxygen consumption, heat production by brown adipose tissue, respiratory rate, and ultrasound production during cold exposure in pups 10-12 days of age. All 3 physiological measures increased contemporaneously with the initiation of ultrasound. Pups also exhibited a respiratory pattern characterized by the prolongation of expiratory duration in relation to inspiratory duration. Ultrasound was often detected during these prolonged expirations, suggesting that pups were using laryngeal braking. Laryngeal braking is thought to enhance oxygen uptake in the lungs. Thus, ultrasound may be an acoustic by-product of a respiratory maneuver that increases oxygen delivery to metabolically active tissues during cold exposure.

The effect of physical work on the mucosal blood flow and gas exchange in the human maxillary sinus

The paranasal sinuses are lined with respiratory mucosa of principally the same structure as in the nasal mucosa but somewhat thinner. This mucosa has a rich blood flow and advanced system of blood vessels regulated mostly by the autonomous nervous system but also by other factors as acid/base balance and endocrine activity. The thickness of the nasal mucosa regulates the nasal breathing resistance and varies with among other factors, body activity. In this investigation we have studied the effect of physical work on the human maxillary sinus mucosa. The investigation shows that, as in the nose, the blood flow and the pulse amplitude are considerably reduced during physical work, in situations of heavy work falling to about half of the normal level, and probably result in the redistribution of blood from the respiratory mucosa. The gas exchange in the paranasal sinus is reduced only to a small extent, the reduction being too small to change the antral gas composition towards pathological conditions.

Respiratory mechanics in the normal dog determined by expiratory flow interruption

We recently proposed an eight-parameter model of the respiratory system to account for its mechanical behavior when flow is interrupted during passive expiration. The model consists of two four-parameter submodels representing the lungs and the chest wall, respectively. The lung submodel consists of an airways resistance together with elements embodying the viscoelastic properties of the lung tissues. The chest wall submodel has similar structure. We estimated the parameters of the model from data obtained in four normal, anesthetized, paralyzed, tracheostomized mongrel dogs. This model explains why lung tissue and chest wall resistances should be markedly frequency dependent at low frequencies and also permits a physiological interpretation of resistance measurements provided by the flow interruption method.

Lung vascular permeability changes in lambs with hyaline membrane disease

To investigate the mechanism of pulmonary edema in hyaline membrane disease (HMD), lymph from the efferent duct of the mediastinal lymph node was collected in premature lambs before and after delivery by cesarean section. Mean lymph flow in 7 lambs with histologically verified HMD increased progressively over 4 h after delivery to 3 times the fetal value, while lymph flow in 7 lambs without HMD increased to 3.5 times at 1 h and decreased thereafter. At 4 h after birth, lung lymph flow was significantly higher in lambs with HMD than in lambs without HMD (0.70 +/- 0.15 (SEM) vs 0.43 +/- 0.07 ml.h-1.kg-1). Lymph/plasma concentration ratio for small endogenous protein fractions (effective molecular radius, 3.6 and 3.8 nm) was significantly higher in lambs with HMD than in lambs without HMD at 2-4 h. Postmortem extravascular lung water was significantly higher in lambs with HMD (6.1 +/- 0.5 vs 4.3 +/- 0.3 ml/g dry lung weight). It is concluded that lung water is high in lambs with HMD, which appears to be a result both of delayed absorption of fetal lung liquid and increased permeability of the pulmonary exchange vessels.